Method of manufacturing prisms, particularly microprisms and beam-splitting prisms

ABSTRACT

The invention relates to a method of manufacturing prisms, particularly microprisms and beam-splitting prisms, including the following steps: a) producing rectangular plates (1), b) fixing a larger number of these plates at their plate surfaces (2) to form a rectangular block (4), c) processing at least one face (support face 5) of the block at a right angle relative to the plate surfaces, d) rearranging the plates of the blocks so that all plate surfaces are aligned at an angle α 1  and that the sharp edges of the plates are placed in contact with the alignment plate (6), e) cementing of several displaced blocks with their cover faces (11) to a carrier body and grinding and polishing the support face (5), f) multiple repetition, if necessary, of steps d) through e) with different angles adjustments α, g) rearranging the plates of the blocks so that all plate surfaces are arranged at an angle β, h) cementing an auxiliary plate (16) to the optically effective surfaces (8, 12), i) cutting off prism strips (18) at a distance a from the surface of the auxiliary plate (16), j) cutting off the microprisms (10), k) detaching the microprisms from the auxiliary plate (16). Very different shapes of microprisms can be produced (FIG. 5).

SPECIFICATION TITLE OF THE INVENTION

Method of manufacturing prisms, particularly microprisms andbeam-splitting prisms

FIELD OF APPLICATION

The invention relates to a method of manufacturing prisms, particularlymicroprisms and beam-splitting prisms, the dimensions of which may be inthe range of μm. Microprisms are used, for example, for the redirectionof beams in endoscopes or for the introduction of light in microopticalor microelectronical structures. The beam-splitting prisms are composedof at least two combined prismatic glass elements with a thin partiallytransparent layer being disposed between the contact surfaces of theelements.

PRIOR ART

U.S. Pat. No. 3,254,556 describes a method for the production ofmicroprisms composed of plates, wherein several plane-parallel platesare stacked with their faces being in contact, wherein the plates aredisplaced relative to each other in such a way that they constitute abody with the outline of a parallelogram.

The plates are fixed with respect to each other in this displacedposition. Thereafter, the resulting body is cut with a saw, wherein theplanes of cutting extend parallel to the inclined face of theparallelogram-shaped body which has the stepped surface structure. Thus,a plurality of microprism plates are obtained from the block ofplane-parallel plates which are offset relative to each other.

From the Japanese specification JP 5-66 303 is known a method for theproduction of prisms that are to be used as beam-splitting prisms,wherein first a plurlity of rectangular plane-parallel plates aremanufactured. On the surface of each plate a thin layer of dielectricmaterial is deposited that later on serves for the splitting of thebeams. Then, a rectangular block is formed by stacking several plateswith their faces in contact, wherein the plates are aligned at two oftheir circumferential sides and their faces. The plates of the resultingrectangular block are displaced relative to each other parallel to theirfaces by a distance that corresponds to the thickness of the plates, sothat a body with parallelogram-shaped cross section is formed. With asubsequent first sawing procedure, the stepped projections are removedfrom one side of the parallelogram-shaped body which projections wereformed by the displacement of the plates, so that a continuous, smoothface is obtained that is polished after the cutting procedure. With thisface the parallelogram-shaped body is fixed to a auxiliary plate, sothat it can be subjected to a further sawing procedure. During sawing,the cuts are oriented perpendicular to the plane of the auxiliary plateand along those lines where the beam-splitting layers hit the auxiliaryplate between the plates. The plate-like elements thus obtained aredivided with two further cutting procedures in such a way that cubicbeam-splitting prisms are obtained.

This procedure is feasible with beam-splitting cubes having generallyused dimensions that can be handled and processed as a single element,but it fails in the case of microoptical components.

OBJECT OF THE INVENTION

New possibilities of application in microoptics and optoelectronicsrequire inexpensive microprisms and beam-splitting prisms in largenumbers. The invention is to solve the problem of manufacturingmicroprisms and beam-splitting prisms with reasonable effort much lessexpensively and as much smaller optical components than usual in thepast. The microprisms and beam-splitting prisms should satisfy highdemands concerning their precision.

DESCRIPTION OF THE INVENTION

In accordance with the invention, the object is met by the features ofclaim 1. Claims 2 to 13 represent advantageous further developments ofthe main claim. The invention relates to a process for the production ofprisms. It is especially desired to inexpensively manufacturemicroprisms or beam-splitting prisms with very variable geometricalshapes.

The prisms are produced from plane-parallel rectangular plates inseveral steps, which partially may be repeated several times withdifferent parameters, e.g. angle settings.

Starting material for the prisms are rectangular plates with parallelplane surfaces on both sides. It is sufficient if the side faces of theplates are cut to size. The dimensions of the sides of the plates shouldbe chosen relatively large. The larger the width b of the supportingside of the plate, the more microprisms can be obtained with oneprocess. The larger the height h, the higher the number of cycles that agiven set of plates can be used in the production of microprisms. Thelarger the height h, the more precise angles of the prisms can beachieved. Normally, the surfaces of the plates are smoothly ground. Ifthe plates are to be fixed by wringing and/or parts of the plates areintended to perform optical functions, then the faces of the plates areadditionally polished. A larger number of plates are fixed with theirfaces to form a rectangular block, wherein the individual plates arealigned according to at least two side faces and the plate surfaces. Forthe highest possible precision, it is advantageous if that side facethat forms the support face is worked in a right angle with respect tothe plate surfaces of the plates, so that a sharp edge is formed betweenthe plate surfaces of the plate and the support face. The number ofplates cemented together results in the length of the block. Fixation ofplates as a block is achieved by a meltable fixation agent or bywringing. By wringing of the plate surfaces a high precision of theangles of the prisms is achieved. In the simplest case, an alignment ofall plates is achieved when the block is formed, with all plate surfacesof the plates being aligned at an angle α₁, which is included betweenthe plane face of the plates and a plane surface of an alignment platethat is part of a device for the adjustment of angles. Edges formed bythe plate surfaces and the side faces of the plates contact the surfaceof the adjustment plate. The highest precision of position is achievedwhen, prior to alignment with the angle α₁, a sharp edge of the block isproduced. This sharp edge is brought into contact with the surface ofthe alignment plate each time the plates are aligned at the angle α onthis surface. The plates of the displaced block are fixed in theirinclined position. Several of the blocks displaced in this manner arecemented to a carrier body with the side of their cover faces and areprocessed by grinding and polishing on the side of their support face.First optically effective surfaces of the prisms are obtained.

If necessary, the alignment of plates is repeated several times withdifferent settings of angles α in order to produce second opticallyeffective surfaces and further surfaces by grinding and polishing. Therearrangement of plates is done after heating of the block by shiftingthe plates in the device for the adjustment of angles or by separatingthe plates from the block and renewed wringing of the plate surfaces ofthe plates. When all optically effective surfaces have been produced onthe side of the support face and/or on the side of the cover face, theplates of the block are rearranged, wherein all plate surfaces of theplates are arranged at an angle β which is enclosed between the planeface of the plate and a plane face of an auxiliary plate. If the angle βis 90°, the thickness of each plate is identical to the hypotenuse ofthe later prism. The auxiliary plate is cemented to the side of theoptically effective surfaces of the plates with the help of a fixationagent. During this process the projecting portions of each plate (itsprojecting tips) contact the surface of the auxiliary plate. Thereafter,prism strips are cut off at a distance a from and parallel to thesurface of the auxiliary plate. After this cutting of prism strips at adistance a from the surface of the auxiliary plate, the exposed cutsurfaces (hypotenuse) in connection with the auxiliary plate areprocessed by grinding and polishing, if needed.

By carrying out parallel sawing cuts that extend at an angle γ withrespect to the prism strips, prisms are obtained. Preferably, the cutsare made at a right angle with respect to the prism strip. In one case,the auxiliary plate is only partially sawed from the side of the prismstrips. Detachment of the prisms from the auxiliary plate is achieved byimmersion into a solvent for the fixation agent.

In a second case, the auxiliary plate is sawed through together with theprism strips. The strips that carry the individual prisms are fixed ontoa carrier in such a way that those faces (triangular faces) that havenot been processed yet are processed by grinding and/or polishing.Thereafter, the prisms are detached from the strips. It is advantageousif in the course of production of the block, additionally to the supportface, a cover face and/or an alignment face are processed by grindingand polishing in such a way that these faces are perpendicular to theplate surfaces of the plates. The processed cover face extends parallelto the support face. Due to the symmetry between the support and coverfaces after angular alignment of all plates into an angular position α,additionally to the support face, the cover face can be processed.First, an optically effective face is produced at the support side ofthe plurality of blocks that are cemented onto a carrier body.Subsequently, after re-cementing to the side of the support faces on thecarrier body, preferably the same optically effective surface isproduced at the cover face. This procedure is repeated for every angularposition α in order to obtain multi-faced prisms. Furthermore, anauxiliary plate is cemented to the cover face that is located oppositethe support side. Also in this case, prism strips are cut off (bysawing) at a distance a from the surface of the auxiliary plate,followed by the further steps described above.

The process according to the invention makes it possible to produceprisms, especially microprisms, relatively inexpensively and with highquality. The technology according to the invention ensures a very goodutilization of material and a high yield of good products. Large numberscan be produced relatively inexpensively in comparison to the knownmethods.

Beam-splitting prisms are obtained by the procedure described above iftwo individual plates are non-displaceably connected to each other so asto form a pair of plates, and a plurality of these pairs of plates aredisplaceably and detachably connected to each other.

The firm connection of the two plates belonging to a pair of plates isachieved, for example, by a heat-resistant cement between the faces ofthe plates. Between the rigidly connected plate surfaces of the plates athin layer is embedded that produces the splitting of an incident beam.This thin layer is produced, for example, by vapor deposition onto thesurface of the plate. The second plane face of the plate attached bycement protects the sensitive thin layer securely against damage duringthe following steps of processing.

According to the intended use of the beam-splitting device, theindividual plates of a pair of plates may have the same thickness--e.g.when used as a beam-splitting cube--or they can be of differentthickness--e.g. when used as a beam-splitting device in a binoculartube.

The invention is described in the following with the help of theFigures. The Figures show:

FIG. 1: plate

FIG. 2: vertically aligned block

FIG. 3: displaced block, angle α₁

FIG. 4: displaced block, angle α₂

FIG. 5: aligned block with cemented auxiliary plates

FIG. 6: prism strips on auxiliary plate

FIG. 7: prisms separated by sawing

FIGS. 8-15: shapes of prisms

FIG. 16: beam-splitting device

FIG. 17: alignment device

FIGS. 1 to 7 show the individual steps of the manufacture of microprismsby a gluing method. FIG. 1 shows an individual plate 1. The platesurfaces 2 are parallel to each other and ground and polished so as tobe plane. The dimensions of the plates should be chosen relativelylarge; a large width b to obtain as many individual microprisms aspossible, and a large height h to be able to carry out as manyprocessing cycles as possible with precise angles of the prisms. Theside faces 3 are cut to size. At a thickness d of 1 mm each, thirty ofthese plates 1 are connected to each other on their smoothly groundplate surfaces 2 with the help of a meltable fixation agent in such away that a block 4 according to FIG. 2 is produced. During gluing theplates are aligned with their plate surfaces 2 extending parallel toeach other. The side faces 3, designated as support face 5, cover face11, and alignment face 19 in the following, are so smoothly ground thatthese side faces extend at a right angle to the plate surfaces 2. Indoing so, the dimension h between the support face 5 and the cover face11 is exactly ground across the whole length of the block 4.

It is important that a sharp edge for the later alignment of the plates1 in the block 4 is obtained between the plate surfaces 2 of the platesand the support face 5 or the cover face 11, respectively.

According to FIG. 3, the block 4 prepared in this manner is placed ontoan angle-adjustment device 14 (see FIG. 16) while it is still warm, andthe plates 1 are displaced in such a way that all plates are aligned onan angle standard 15 at the angle α₁. All projecting sharp edges thatare formed by the plate surfaces 2 and the support faces 5 are incontact with the plane surface of the alignment plate 6, and an exposedplate surface 2 of the block is in contact with the face of the anglestandard 15. Consequently, all plates 1 of a block 4 have the sameinclination. Several displaced and cooled blocks of equal height h arecemented with the side of their cover faces 11 to a carrier body in sucha way that the side of the blocks with the support faces 5 is exposedfor processing (not shown). The blocks 4 are processed together bygrinding and polishing them up to the polishing plane 20.

Due to the existing symmetry, first optically effective surfaces 8 canbe produced at the side of the support faces 5, and after re-cementingthe blocks 4 at the side of the support faces 5 the same processingsteps can be carried out at the cover face 11. Equal prisms are obtainedas a result.

If plane surfaces are produced at the displaced blocks in the polishingplane 20, the plate surfaces 2 of the plates 1 are with sharp edges incontact with the first optically effective surface 8 (see FIG. 8).

If the projecting tips of the displaced plates of the block are notentirely removed, a first optically effective surface 8 results whichforms a sharp boundary with the remaining support face 5 or the coverface 11, respectively (see FIG. 9). In this case, if necessary, thesupport face 5 (or the cover face 11, respectively) may be polishedbefore displacing the plates in the block (see FIG. 2).

The processing steps depicted in FIG. 3 and described above can berepeated with various arbitrary angles α in the range between theextreme values 0° and 180° in order to produce second opticallyeffective surfaces 12.

FIG. 4 shows the processing of a second optically effective surface 12.In the example, the angle α₂ is produced, which is equal to the angleα₁. The angle φ of the prism results from the angles α₁ plus α₂. Theplane of polishing 20 is chosen in such a way that isosceles prism facesresult. After processing of the last optically effective surface, theplate surfaces 2 of the plates 1 of a block 4 are heated and alignedaccording to an angle β which, in the example, is 90° relative to theplane surface of the auxiliary plate 16, in order to obtain isoscelesprisms (see FIG. 11).

According to FIG. 5, auxiliary plates 16 are fixed with a fixation agent7 on those sides of the blocks that carry the optically effectivesurfaces. At a distance a from each auxiliary plate 16 a cut 13 bysawing parallel to the auxiliary plate 16 is made. The distance a isdimensioned such that prism strips 18 result which have, in the example,no more residual parts of plane surfaces 2. The resulting cut faces 9are the hypothenuse faces of the prism strips 18 which are subsequentlypolished together with the auxiliary plate 16 (see FIG. 6).

Thereafter, the prism strips 18 that are cemented to the auxiliary plate16 are cut into prisms under the cutting angle γ, which is 90° in theexample (see FIG. 7). The cutting angle γ determines the angularposition of these cut faces relative to the faces 2, 8, 9, and 12.

If the auxiliary plate is only partially sawed from the side of theprism strips 18, individual prisms can be removed after the immersion ofthe auxiliary plate into a solvent for the fixation agent. If theauxiliary plate with the supporting microprisms is cut through bysawing, the microprisms firmly attached to the auxiliary plate aresupported in such a way that, if necessary, the cut faces (front andrear triangle faces) may be processed by grinding and/or polishing.

FIGS. 8 to 15 show several examples of prism shapes that can be obtainedby the method according to the invention. If necessary, the front andrear faces of all prisms that are depicted in side views can beprocessed to be optically effective. According to FIG. 8, the platesurface 2, the first optically effective surface 8, and the cut face 9can be optically effective surfaces. In FIG. 9, the supporting surface 5additionally is an optically effective surface. In FIG. 10, the secondoptically effective surface is additionally produced. FIG. 11 depicts aisosceles prism having a first optically effective surface 8 and asecond optically effective surface 12. Again in this case, the cut face9 can be an optically effective surface. In the prism depicted in FIG.12, the angle β between the plate surface 2 and auxiliary plate 16 (seeFIG. 5) does not equal 90°. The sawing cut 9 parallel to the auxiliaryplate 16 produces a parallelogram-shaped prism having the faces 2, 8, 2,and 9, each of which may be optically effective surfaces if needed. FIG.13 shows a prism with the faces 2, 8, 12, 2, and 9, each of which may beoptically effective if needed. FIG. 14 shows a prism with the faces 2,8, 12, and 9. FIG. 15 shows a prism with the faces 2, 8.1, 8.2, 5, 12.1,12.2, 2, and 9.

The first optically effective surfaces 8.1, 8.2 and the second opticallyeffective surfaces 12.2, 12.2, are produced by different angularpositions α. The possibilities of prism shapes shown in FIGS. 8 to 15are certainly not complete. The shapes can be combined with each otherand modified. The illustrations represent a selection of the multitudeof possibilities to produce prisms by the method of this invention.

FIG. 16 schematically represents the processing steps for manufacturingbeam-splitting prisms. FIG. 16a shows composite pairs of plates 2 whichare displaceable relative to each other and enclose a transparent layer21 between them. FIG. 16b shows the displaced pairs of plates 2 with afirst optically effective surface 8 being processed to a final stage(polished). FIG. 16c depicts the position of the pairs of plates afterre-cementing into another angle and with a second optically effectivesurface 12 obtained by grinding and polishing. According to FIG. 16d thesecond optically effective surfaces 12 of the pairs of plates arecemented to an auxiliary plate 16. By means of cutting by sawing,subsequent grinding, and polishing, a third optically effective surfaceis produced in the plane of polishing 20. If the outer surfaces of theplates possess optical quality, individual beam-splitting prisms areobtained after cutting the prism strips 18 horizontally with respect tothe plane of the drawing, wherein the individual beam-splitting prismscan be used in a binocular tube.

A beam-splitting cube according to FIG. 16f is obtained by processing aforth optically effective surface. This is done by separating the prismstrips of FIG. 16d and cementing them to a further auxiliary plate 16with their first optically effective surfaces, as shown in FIG. 16e.After grinding and polishing in the plane of polishing 20, the prismstrips 18 are cut in the plane of the drawing, yielding individualbeam-splitting cubes.

FIG. 17 shows a device for the alignment of blocks 4 according to theangle α. This angular alignment device is composed of a planar alignmentplate 6 on which the angular standard 15 is placed. For the lateralalignment of the plates 1 of a block 4, the angular alignment device 14has a stop 17. The plates 1 are aligned with their alignment faces 19 atthe stop 17. A plate surface 2 of a plate 1 rests on the angle standard15. A sharp edge formed by the plate face 2 and the support face 5 is incontact with the surface of the alignment plate 6. The further plates 1are in contact with each other via their plate surfaces 2 and thusreceive the same orientation.

The method has been described with the example of microprisms. However,the method is also well suited for the production of prisms as the areusually produced and the dimensions of which are in the order ofcentimeters.

REFERENCE NUMERALS

1 plate, pair of plates

2 plate surface

3 side face

4 block

5 support face

6 alignment plate

7 fixation agent

8 first optically effective surface

9 plane of cut (hypotenuse)

10 microprism

11 cover face

12 second optically effective surface

13 sawing cut

14 angular alignment device

15 angle standard

16 auxiliary plate

17 stop

18 prism strip

19 alignment face

20 polishing plane

21 transparent layer

a distance

b width of plate

c thickness of plate

d height of plate

l length of block

α angle between plate surface (2) and support face (5)

β angle between plate surface (2) and surface of the auxiliary plate(16)

φ angle of prism

γ angle of cut

I claim:
 1. A method of manufacturing prisms, particularly microprismsand beam-splitting prisms, from rectangular plane-parallel plates,including the steps of:a) producing rectangular plates, each platehaving plane-parallel plate surfaces, a support face, and a cover face;b) stacking a plurality of these plates on top of each other on theirplate surfaces, wherein the plates are aligned on at least two of theirside faces and on their plate surfaces to form a rectangular block; c)placing all plates of the block into an inclined arrangement plate, suchthat each of the plates of the block lie with a support face edge onsaid plane alignment plate, and that all plate surfaces assume apredetermined first angle relative to the plane surface of the alignmentplate, and fixing the plates in their position of relative displacement;d) cementing a carrier body onto several blocks with inclined platesthat have been produced according to steps a) to c), wherein the carrierbody is cemented to the stepped cover faces of the inclined plates; e)grinding and polishing the projecting support faces of the exposed sideof the blocks for producing optically effective projecting parts; f)repeating steps c) through e) several times with inclinations differingfrom said first angle, and repeating step e) to produce furtheroptically effective projecting parts by grinding and polishing; g)rearranging the plates of the blocks such that all plate surfaces arearranged at a predetermined angle with respect to the plane surface ofan auxiliary plate; h) cementing the auxiliary plate to the blocks atthe side with the optically effective projecting parts, wherein theprojecting parts of the individual plates are placed on the surface ofthe planar auxiliary plate; i) cutting a plate of prism strips out ofthe blocks by sawing the blocks in a plane parallel to the plane of theauxiliary plate, the plane of cutting within the blocks being arrangedsuch that its distance to the projecting parts of the opticallyeffective surfaces on the auxiliary plate corresponds to the height ofthe prisms; j) cutting individual prisms by sawing the prism strips withcuts that are parallel to each other at a predetermined angle relativeto the longitudinal direction of the prism strips; and k) detaching thecut prisms from the auxiliary plate.
 2. The method according to claim 1,comprising producing the plate surfaces by smooth grinding.
 3. Themethod according to claim 1, comprising producing the plate surfaces bysmooth grinding and polishing.
 4. The method according to claim 1,comprising fixing the plates stacked according to step (b) to form ablock using a meltable fixation agent.
 5. The method according to claim1, comprising fixing the plates stacked according to step (b) to form ablock by wringing.
 6. The method according to claim 1, comprisingcarrying out the rearrangement of the plates according to step (g) afterheating the block by displacing the individual plates.
 7. The methodaccording to claim 1, comprising carrying out the rearrangement of theplates according to step (g) by separating the plates from the block andby wringing.
 8. The method according to claim 1, wherein the angle ofrearrangement according to step (g) is 90°, whereby a thickness of eachplate equals the hypotenuse of the prism.
 9. The method according toclaim 1, wherein the side faces have edges, the edges of the side facesresting on the alignment plate according to step (c) including a rightangle with the plate surface next to the side edge, and wherein sharpedges resulting from the inclined placement of the plates are in contactwith the surface of the alignment plate.
 10. The method according toclaim 9, comprising additionally smooth grinding an oppositely locatedor another side face such that the face extends at a right anglerelative to the plate surfaces.
 11. The method according to claim 9,comprising additionally smooth grinding and polishing an oppositelylocated or another side face such that the face extends at a right anglerelative to the plate surfaces.
 12. The method according to claim 10,comprising, after carrying out step (e), cementing the carrier body tothe side of the block having the optically effective surfaces, andproducing optically effective surfaces by grinding and polishingprojecting parts of the single plates on an exposed side.
 13. The methodaccording to claim 10, comprising, after carrying out step (f),cementing the carrier body to the side of the block having the opticallyeffective surfaces, and producing optically effective surfaces bygrinding and polishing projecting parts of the single plates on anexposed side.
 14. The method according to claim 12, comprising, afterproducing the optically effective surfaces, cementing an auxiliary plateto an exposed side of the block, and cutting a plate of prism strips bysawing the block in a plane parallel to the plane of the auxiliaryplate, and choosing the plane of sawing such that a distance of theplane to the parts of the optically effective surfaces projecting on theside of the block corresponds to the height of the prism.
 15. The methodaccording to claim 1, comprising carrying out the sawing cuts of step(j) at a right angle to the prim strips.
 16. The method according toclaim 1, comprising, after cutting off the plate of prism strips,processing exposed cutting planes of the prism strip together with theauxiliary plate by grinding and polishing.
 17. The method according toclaim 1, comprising carrying out step (j) by only partially sawing theauxiliary plate from the side of the prism strips and fixing the stripscarrying the single prisms on a carrier body such that not yet processedside faces of the prisms can be processed by at least one of grindingand polishing.
 18. The method according to claim 1, comprising carryingout step (j) by sawing through the auxiliary plate from the side of theprism strips and fixing the strips carrying the single prisms on acarrier body such that not yet processed side faces of the prisms can beprocessed by at least one of grinding and polishing.
 19. The methodaccording to claim 1, comprising indisplacably connecting two plates toeach other to form a pair of plates, and embedding a thin layer betweenconnected plate surfaces, wherein neighboring pairs of plates aredisplacable with respect to each other.